This invention relates generally to the field of optical scanning or reading and specifically to the structure of an optical system that is particularly suitable for use in a hand-held probe for scanning bar codes.
The use of bar codes to provide information on product prices, identity, and inventory levels is a well-established practice in retail businesses and elsewhere because bar codes are convenient, inexpensive, and lend themselves well to semi or full automation reading techniques.
In bar codes, information is stored as alternating dark and light stripes, the width and spacing of which are used as a means of encoding. When properly illuminated with a small enough beam of light, they return a modulated reflected beam of light which, if sufficiently intense, can be detected and converted to electrical form for decoding purposes. Usually, the bar code is scanned with a beam of illumination and the reflected beam simultaneously detected with an optical system of sufficient resolution. During scanning, the bar code is moved relative to the detection system, and relative motion is achieved by either moving the coded product relative to a fixed scanning head, most often seen in a supermarket, or by moving a hand-held probe over the code on the product, more often seen in lower volume retail situation.
The performance of hand-held probes should be reasonably insensitive to their rotational and angular attitudes and, as well, to their proximity to a bar code because such positional variations are to be expected in hand operations. In addition, signal strength, resolution, noise level, and ease and cost of fabrication are important considerations in the design and manufacture of scanners, whether hand-held or fixed types.
Prior art hand-held probe devices have included fiber optic illumination systems along with a lens system that is structured to focus reflected light onto a sensing module as shown, for example, in U.S. Pat. No. 3,916,184 issued to Thomas W. Turner on Oct. 28, 1975 and entitled "Optical Scanner in Modular Form". In U.S. Pat. No. 3,784,794 issued to David C. Allais on Jan. 8, 1974 and entitled "Electro-Optical Reader for Bar Codes or the Like", a hand-held probe is disclosed which utilizes as an optical system, for both the illumination and detection of reflected light from the bar code, a spherical lens on the rear surface of which is positioned either one or more detectors.
A dual focusing system for use in a hand-held bar code probe is disclosed in U.S. Pat. No. 4,143,809 issued to John J. Uebbing et al on Mar. 13, 1979 and entitled "Optical Bar Code Reader". Here, a pair of discrete lenses are integrally molded aside of one another as part of a support with their optical axes intersecting at a predetermined acute angle. The surfaces of the lenses are in the form of hyperbolic sections that are selectively shaped to eliminate spherical aberration.
In spite of the many innovations made in this art, improved hand-held bar code probes are still required and can be usefully employed for a variety of purposes. In particular, optical systems are required for use in hand-held probes to provide signals of high strength and low noise while at the same time being able to resolve to levels required in a variety of positions and spacings from the bar code. Furthermore, ease and efficiency of manufacture and the use of simple structures are important considerations in the design of bar code scanners. Accordingly, it is the primary object of the present invention to provide an optical system for use in the hand-held bar code probe having the above beneficial characteristics.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. The invention accordingly comprises the structure exemplified in the detailed disclosure which follows.